From: Helmut Hlavacs Newsgroups: comp.parallel.pvm Subject: Transmission time for Beowulf varies Date: Thu, 25 Mar 1999 17:16:30 +0100 Organization: Vienna University, Austria Message-Id: <36FA615E.FC7FE8F2@ani.univie.ac.at> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Xref: ukc comp.parallel.pvm:8192 Hi! Maybe, somebody can help me: I am executing a simple parallel master-slave algorithm running on a Linux Beowulf cluster consisting of 5 workstations, each containing 2 Pentium II 350 MHz. The OS is Linux 2.2.1 SMP Kernel (SuSE), PVM3.4. The network consists of a swtiched ethernet with cards 3Com Fast-Etherlink 3C905-TX. I now observe a strange behavior: Basically, the network is very fast and messages need only a very small time to arrive (<2/10000 sec per KB). But: If there are tasks running on both CPUs at the receiver's workstation, then there is a 1/3 chance that the message needs about 0.15 seconds!.If there is only one receiver task, then the transmission time is near constant. This is true for both tasks on both processors, thus it is not one task taking away CPU time from the pvmd. This is of interest for me because I am simulating such executions, and varying transmission times are difficult to simulate. Does anybody have any idea, why this happens? Helmut -- Dipl.Ing. Helmut Hlavacs Institute for Applied Computer Science and Information Systems Lenaug. 2, 1080 Vienna, Austria. Tel.: 408 63 66 / 22 Fax.: 408 04 50 e-mail: hlavacs@ani.univie.ac.at